Information recording method, information recording medium, and information recording apparatus

ABSTRACT

An information recording apparatus having an energy beam generator for generating an energy beam, a power adjusting mechanism for setting a power level of the energy beam to a first power level state and a second power level state which is higher than the first power level state and a circuit for generating a basic recording pattern to record a recording medium. When a period of a recording timing generating clock in a recording mode is T, and a relative velocity of the energy beam and the recording medium is v, the circuit forming a sequence of the first and second power level states so as to effect recording.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an information recording method, aninformation recording medium and an information recording apparatus,using a recording medium in which information can be recorded by energybeam irradiation. Particularly, it relates to an information recordingmethod having an excellent effect on a phase-change optical disk, aninformation recording medium, and an information recording apparatususing the information recording method.

2. Description of the Related Art

In the case of using, for example, such a photo-magnetic disk asdescribed in JP-A-62-175948 having a switched connection two-layer filmas a recording film, or in the case of using, for example, such ahigh-speed erasable recording film for a phase-change optical disk asdescribed in JP-A-62-259229 capable of performing crystallization inalmost the same time as laser irradiation time for recording, aconventional recording/erasing method on a rewritable recording film iscarried out by changing a power level of an energy beam between at leasttwo power levels (that is, at least a high power level and anintermediate power level) which are higher than a read power level. Theconventional method has an advantage in that new information can berecorded while existing information is erased, that is, overwriting(rewriting owing to overwriting) can be made. Further, such a phenomenonthat a recording mark is shaped like a teardrop (a rear portion of arecording mark becomes wider than a front portion of the recording mark)can be suppressed by changing a power level of an energy beam amongthree power levels consisting of a high power level, an intermediatepower level and a low power level lower than the intermediate powerlevel as described in JP-A-62-259229 and JP-A-3-185629.

On the other hand, recently, a DVD-RAM using a phase-change material toachieve a memory capacity of 2.6 GB per side in a 120 mm-diameter diskhas been put into practical use. A recording control method used in theDVD-RAM is described in JIS Standard, JIS X 6243 for 120 mm DVDRwritableDisk (DVD-RAM) (hereinafter referred to as “Standard Book JIS X 6243”),page 86. Control based on the aforementioned three power levels isdescribed in the standard book.

Researches into improvement of the density of a rewritable digital videodisk (DVD-RAM) using a phase-change recording film are in progress. Inan optical disk device such as a DVD-RAM in which mark edge recording isperformed in a phase-change recording film, both attained temperatureand cooling speed in a recording mode need to be made substantiallyuniform in every place of an outer edge portion of a recording-filmfused region for forming recording marks in the recording film in orderto prevent both mark shape distortion and incomplete erasure. However,in various types of known recording waveforms, it is impossible tosatisfy the condition sufficiently. Accordingly, there is a limitationin realizable recording density. Further, recording characteristic of arecording medium usually varies according to the producer, productiontime and lot of the recording medium. Accordingly, there is a tendencyfor recording compatibility to be more hardly secured as higher-densityrecording is intended.

Particularly, in a DVD-RAM with a memory capacity of 4.7 GB higher indensity than the DVD-RAM with a memory capacity of 2.6 GB, recording isperformed with the same spot diameter as that in the 2.6 GB DVD-RAM sothat the compatibility with 2.6 GB DVD-RAM can be kept easily. However,when linear density is increased while the spot diameter is keptconstant, the distance between positions irradiated on a recordingmedium by two recording pulses adjacent to each other is reducedcompared with the light spot diameter of laser light on the recordingmedium. Accordingly, light distributions overlap each other comparedwith the 2.6 GB DVD-RAM, so that it is necessary to prevent therecording mark shape from being distorted due to the overlapping oflight distributions. Therefore, it is thought of that more complicatedmodulated recording waveform control is used to increase the number ofpower levels so as to change the energy beam among four power levels. Insuch a complicated recording waveform, good-shape recording marks can beformed if appropriate setting is performed. Increase of the number ofenergy levels, however, brings about a problem of how to optimize therespective energy levels. That is, when the respective energy levels areset appropriately, good recording marks having little recording markshape distortion can be formed. But, there is a problem that theprocedure of optimizing the energy levels is complicated because energybalance becomes delicate and the number of energy levels is large (firstproblem).

In the conventional recording/erasing method applied to the rewritablerecording film as described in the aforementioned Standard Book JIS X6243, page 86, the control on the basis of the aforementioned threepower levels is described. The recording power levels used in therecording mode are written in a control data area on the disk. Theinformation recording apparatus sets the recording power levels byreading the recording power levels written on the disk. The absolutevalues of the recording power levels, however, may change due to theindividual difference of the information recording apparatus, or due tothe environmental change or aging of the information recordingapparatus. In most cases, therefore, the recording power levels arechecked or adjusted before information is written in the disk actually.That is, while Peak Power is changed in a condition that Bias Power 1and Bias Power 2 given to the control data area are fixed, a randompattern is recorded and then reproduced to measure reproductive jitter.The recording power level to make the value of reproductive jitter equalto a predetermined value is multiplied by a predetermined factor so thata recording power level is obtained. The recording power level obtainedthus is set as new Peak Power. Then, while Bias Power 1 is changed, therandom pattern is recorded and then reproduced to measure thereproductive jitter. The bias power to minimize the value of thereproductive jitter is set as new Bias Power 1.

In a phase-change recording medium of a 120 mm diameter with a largercapacity than 2.6 GB per side (for example, a DVD-RAM with a diameter of120 mm intended to achieve a capacity of 4.7 GB per side), accurateinformation recording may be performed by adaptively changing the timingof leading and trailing edge portions of a recording pulse in accordancewith the combination of recording patterns to be recorded. It is thoughtof that such timing information is recorded in the control data area onthe disk so that the information recording apparatus reads the timinginformation to use it for actual recording.

The information recording apparatus does not always have the samerecording characteristic. The recording characteristic may change due tothe individual difference of the information recording apparatus, or dueto the aging or environmental change of the information recordingapparatus. Accordingly, it may be impossible to perform appropriaterecording on the basis of the timing information written on the disk. Insuch a case, the reproductive jitter at the time ofrecording/reproducing the random pattern becomes worse than the expectedvalue. As a result, if the recording power levels are determined on thebasis of the jitter of the random pattern in the same manner as that inthe prior art, there is a possibility that the recording power levelsmay be set to unsuitable values. If the recording is performed on thebasis of the unsuitable recording power levels, there is a fear ofreduction in reliability of recording/reproducing, for example, therecording becomes unstable, the already written information is eraseddue to cross-erasure, and so on (second problem).

Further, as described above, in the DVD-RAM with the recording capacityof 4.7 GB which is higher in density than the 2.6 GB DVD-RAM, therecording can be performed with the same spot diameter as that in the2.6 GB DVD-RAM so that the compatibility with the 2.6 GB DVD-RAM can beobtained. However, when the linear density is made high while the spotdiameter is kept unchanged, the distance between two positions on therecording medium irradiated with two adjacent recording pulses isreduced compared with the light spot diameter of laser light on therecording medium. For this reason, the light distributions overlap eachother compared with the case of 2.6 GB, so that it is necessary toprevent the recording mark shape distortion due to the overlapping ofthe light distributions. Further, when the space between the recordingmarks is short, the recording marks cannot be resolved by the readinglight spot, so that the shifting of the recording mark edge positionoccurs in the reproductive signal waveform. Accordingly, it is alsonecessary to prevent the recording mark edge position from shifting. Forthis reason, an attempt has been made to reduce the shifting of therecording mark edge position by changing the irradiation timing of therecording pulses according to the length of a mark to be written and thelength of a portion (hereinafter referred to as “space”) between marks.However, when high-density recording is to be performed by use of thephase-change medium such as a DVD-RAM with the recording capacity of 4.7GB, there is a problem that the procedure for determining theirradiation timing of the recording pulses in detail is not always clear(third problem).

SUMMARY OF THE INVENTION

A first object of the present invention is to solve the aforementionedfirst problem, that is, to provide an information recording method andan information recording apparatus in which the accurate recording canbe performed to improve density more greatly by use of the same spotdiameter as that in the prior art while the compatibility with the priorart is kept. Particularly, the first object of the present invention isto provide an information recording method in which four energy levelsfor use in forming recording marks are selected easily and accurately,and to provide an information recording apparatus using the informationrecording method.

A second object of the present invention is to solve the aforementionedsecond problem, that is, to provide an information recording method andan information recording apparatus in which such unsuitable recordingpower levels as mentioned above are prevented from being set so that thestable recording/reproducing can be normally performed.

A third object of the present invention is to solve the aforementionedthird problem, that is, to provide an information recording method, aninformation recording medium and an information recording apparatus inwhich the accurate recording can be performed to improve the densitymore greatly by use of the same spot diameter as that in the prior artwhile the compatibility with the prior art is kept. Particularly, thethird object of the present invention is to provide a procedure foraccurate measuring the irradiation timing of the recording pulse and aprocedure for determining the optimum irradiation timing, an informationrecording apparatus using the measuring and determining procedures ofthe irradiation timing, and an information recording medium in which theirradiation timing determined using the measuring and determiningprocedures of the irradiation timing are recorded as fixed information.

To solve the aforementioned first problem, the following informationrecording method and apparatus may be used.

(1) An information recording method using a recording medium permittedto get into a first state by a first power level of an energy beam andpermitted to get into a second state by a second power level of theenergy beam higher than the first power level, for recording informationon the recording medium by moving the energy beam and the recordingmedium relatively to each other so that the recording medium isirradiated with the energy beam and the first and second states areformed on the recording medium with predetermined lengths and atpredetermined intervals, comprising the steps of:

providing a third power level equal to or less than the first powerlevel;

making a period of the third power level coexistent with a period of thesecond power level to multi-pulsate the energy beam and irradiating therecording medium with the multi-pulsated energy beam when a region ofthe second state is formed in the recording medium so that the region ofthe second state has a specific length;

providing a fourth power level equal to or less than the first powerlevel;

irradiating the recording medium with the fourth power level of theenergy beam for a predetermined period following the last pulse of themulti-pulsated energy beam;

multiplying the second power level by a magnification factor x tothereby obtain a new second power level;

multiplying the first power level by a magnification factor y to therebyobtain a new first power level;

multiplying the third power level by the magnification factor y tothereby obtain a new third power level;

multiplying the fourth power level by the magnification factor y tothereby obtain a new fourth power level;

recording information on the recording medium while changing values ofthe magnification factors x and y variously, and reproducing therecorded information to thereby obtain a reproductive signal; and

adjusting the values of the magnification factors x and y so that avalue of reproductive jitter of the reproductive signal is less than apredetermined value.

(2) An information recording method using a recording medium permittedto get into a first state by a first power level of an energy beam andpermitted to get into a second state by a second power level of theenergy beam higher than the first power level, for recording informationon the recording medium by moving the energy beam and the recordingmedium relatively to each other so that the recording medium isirradiated with the energy beam and the first and second states areformed on the recording medium with predetermined lengths and atpredetermined intervals, comprising the steps of:

providing a third power level equal to or less than the first powerlevel;

making a period of the third power level coexistent with a period of thesecond power level to multi-pulsate the energy beam and irradiating therecording medium with the multi-pulsated energy beam when a region ofthe second state is formed in the recording medium so that the region ofthe second state has a specific length;

providing a fourth power level equal to or less than the first powerlevel;

irradiating the recording medium with the fourth power level of theenergy beam for a predetermined period following the last pulse of themulti-pulsated energy beam;

multiplying the first power level by a magnification factor z to therebyobtain a new first power level;

multiplying the second power level by the magnification factor z tothereby obtain a new second power level;

multiplying the third power level by the magnification factor z tothereby obtain a new third power level;

multiplying the fourth power level by the magnification factor z tothereby obtain a new fourth power level;

recording information on the recording medium while changing values ofthe magnification factor z variously, and reproducing the recordedinformation to thereby obtain a reproductive signal; and

adjusting the value of the magnification factor z so that a value ofreproductive jitter of the reproductive signal is less than apredetermined value.

(3) An information recording apparatus comprising:

an energy beam generator for generating an energy beam;

a power adjusting mechanism for setting a power level of the energy beamto a first power level and a second power level which is higher than thefirst power level;

a holding mechanism for holding a recording medium permitted to get intoa first state by the first power level and permitted to get into asecond state by the second power level;

a moving mechanism for moving the energy beam and the recording mediumrelatively to each other;

a positioning mechanism for irradiating a predetermined place of therecording medium with the energy beam; and

a signal processing circuit for changing information to be recorded,into the power levels of the energy beam;

the power adjusting mechanism including:

-   -   a function of making a period of a third power level coexistent        with a period of the second power level to thereby multi-pulsate        the energy beam when a region of the second state is formed in        the recording medium so that the region of the second state has        a specific length, the third power level being equal to or less        than the first power level;    -   a function of irradiating the recording medium with the energy        beam of a fourth power level for a predetermined period        following a last pulse of the multi-pulsated energy beam, the        fourth power level being equal to or less than the first power        level;    -   a function of setting the second power level multiplied by a        magnification factor x to a new second power level;    -   a function of setting the first power level multiplied by a        magnification factor y to a new first power level;    -   a function of setting the third power level multiplied by the        magnification factor y to a new third power level; and    -   a function of setting the fourth power level multiplied by the        magnification factor y to a new fourth power level; and

the information apparatus further comprises:

-   -   means for forming the first and second states on the recording        medium by irradiating the recording medium with the energy beam        while changing values of the magnification factors x and y        variously;    -   a time interval measuring circuit for measuring fluctuation of a        reproductive signal obtained by reproducing the first and second        states; and    -   a controller for adjusting the values of the magnification        factors x and y so that the value of the fluctuation of the        reproductive signal obtained by the time interval measuring        circuit is less than a predetermined value.        (4) An information recording apparatus comprising:

an energy beam generator for generating an energy beam;

a power adjusting mechanism for setting a power level of the energy beamto a first power level and a second power level which is higher than thefirst power level;

a holding mechanism for holding a recording medium permitted to get intoa first state by the first power level and permitted to get into asecond state by the second power level;

a moving mechanism for moving the energy beam and the recording mediumrelatively to each other;

a positioning mechanism for irradiating a predetermined place of therecording medium with the energy beam; and

a signal processing circuit for changing information to be recorded,into the power levels of the energy beam;

the power adjusting mechanism including:

-   -   a function of making a period of a third power level coexistent        with a period of the second power level to thereby multi-pulsate        the energy beam when a region of the second state is formed in        the recording medium so that the region of the second state has        a specific length, the third power level being equal to or less        than the first power level;    -   a function of irradiating the recording medium with the energy        beam of a fourth power level for a predetermined period        following a last pulse of the multi-pulsated energy beam, the        fourth power level being equal to or less than the first power        level;    -   a function of setting the first power level multiplied by a        magnification factor z to a new first power level;    -   a function of setting the second power level multiplied by the        magnification factor z to a new second power level;    -   a function of setting the third power level multiplied by the        magnification factor z to a new third power level; and    -   a function of setting the fourth power level multiplied by the        magnification factor z to a new fourth power level; and

the information apparatus further comprises:

-   -   means for forming the first and second states on the recording        medium by irradiating the recording medium with the energy beam        while changing a value of the magnification factors z variously;    -   a time interval measuring circuit for measuring fluctuation of a        reproductive signal obtained by reproducing the first and second        states; and    -   a controller for adjusting the value of the magnification factor        z so that the value of the fluctuation of the reproductive        signal obtained by the time interval measuring circuit is less        than a predetermined value.

To solve the aforementioned second problem, the following informationrecording method and apparatus may be used.

(1) An information recording method using a recording medium permittedto get into a first state by a first power level of an energy beam andpermitted to get into a second state by a second power level of theenergy beam higher than the first power level, for recording informationon the recording medium by forming the first and second states withpredetermined lengths and at predetermined intervals on the recordingmedium by changing a power level of the energy beam among a plurality ofpower levels including the first and second power levels according toinformation to be recorded while moving the energy beam and therecording medium relatively to each other so that the recording mediumis irradiated with the energy beam to thereby form a pulse string of theenergy beam, the method comprising the steps of:

optimizing the first power level while fixing the second power level toa suitable initial value; and

optimizing the second power level while fixing the first power level tothe optimized value.

(2) An information recording method using a recording medium permittedto get into a first state by a first power level of an energy beam andpermitted to get into a second state by a second power level of theenergy beam higher than the first power level, for recording informationin the recording medium by forming the first and second states withpredetermined lengths and at predetermined intervals on the recordingmedium by changing the energy level among a plurality of power levelsincluding the first and second power levels according to information tobe recorded while moving the energy beam and the recording mediumrelatively to each other so that the recording medium is irradiated withthe energy beam to thereby form a pulse string of the energy beam, themethod comprising:

at least one of a first timing adjusting method for adjusting a timingof a pulse of the energy beam which corresponds to a head portion of thesecond state to be formed on the recording medium, and a second timingadjusting method for adjusting a timing of a pulse of the energy beamwhich corresponds to a tail portion of the second state to be formed onthe recording medium; and

at least one of a first adjusting procedure for adjusting the timingsaccording to the first and second timing adjusting methods afteroptimizing the power levels by the information recording methoddescribed in (1), and a second adjusting procedure for optimizing thepower levels by the information recording method described in (1) afteradjusting the timings according to the first and second timing adjustingmethods.

(3) An information recording apparatus comprising:

an energy beam generator for generating an energy beam;

a power adjusting mechanism for setting a power level of the energy beamto a first power level and a second power level which is higher than thefirst power level;

a holding mechanism for holding a recording medium permitted to get intoa first state by the first power level and permitted to get into asecond state by the second power level;

a moving mechanism for moving the energy beam and the recording mediumrelatively to each other;

a positioning mechanism for irradiating a predetermined place of therecording medium with the energy beam;

a signal processing circuit for changing information to be recorded intothe power levels of the energy beam;

means of optimizing the first power level while fixing the second powerlevel to a suitable initial value and then optimizing the second powerlevel while fixing the first power level to the optimized value tothereby set the power levels in a recording mode.

(4) An information recording apparatus comprising:

an energy beam generator for generating an energy beam;

a power adjusting mechanism for setting a power level of the energy beamto a first power level and a second power level which is higher than thefirst power level;

a holding mechanism for holding a recording medium permitted to get intoa first state by the first power level and permitted to get into asecond state by the second power level;

a moving mechanism for moving the energy beam and the recording mediumrelatively to each other;

a positioning mechanism for irradiating a predetermined place of therecording medium with the energy beam;

a signal processing circuit for changing information to be recorded intothe power levels of the energy beam;

at least one of first and second timing adjusting means, the firsttiming adjusting means adjusting a timing of a pulse of the energy beamcorresponding to a head portion of the second state to be formed on therecording medium, and the second timing adjusting means adjusting atiming of a pulse of the energy beam corresponding to a tail portion ofthe second state to be formed on the recording medium; and

at least one of third and fourth timing adjusting means, the thirdtiming adjusting means performing timing adjustment in the first andsecond timing adjusting means after optimizing the power levels by theoptimization means according to claim 15, and the fourth timingadjusting means optimizing the power levels by the optimizing meansaccording to claim 15 after performing the timing adjustment in thefirst and second timing adjusting means.

To solve the aforementioned third problem, the following informationrecording method and apparatus may be used.

(1) An information recording method using a recording medium permittedto get into a first state by a first power level of an energy beam andpermitted to get into a second state by a second power level of theenergy beam higher than the first power level, for recording informationon the recording medium by moving the energy beam and the recordingmedium relatively to each other so that the recording medium isirradiated with the energy beam and the first and second states areformed on the recording medium with predetermined lengths and atpredetermined intervals, comprising the steps of:

when a period of a recording timing generating clock in a recording modeis T, and a relative velocity of the energy beam and the recordingmedium is v,

forming a sequence of the second state with length avT (first mark), thefirst state with length ivT (first space) following the first mark, thesecond state with length mvT (second mark) following the first space,the first state with length jvT (second space) following the second markand the second state with length bvT (third mark) following the secondspace as a first small recording pattern;

forming a sequence which starts with the first state and ends with thefirst state while the first and second states appear alternately by afinite number of times, as a second small recording pattern;

forming a state in which the second small recording pattern follows thefirst small recording pattern, as a basic recording pattern;

forming a state in which the basic recording patterns are repeated, as arecording pattern;

forming the recording pattern which comprises the basic recordingpatterns obtained by changing a parameter i variously while parametersa, i and m are fixed, as a first recording pattern, the parameters a, i,m and j being natural numbers;

forming the recording pattern which comprises the basic recordingpatterns obtained by changing the parameter i variously while aparameter b and the parameters j and m are fixed, as a second recordingpattern, the parameter b being a natural number; and

using at least one of first and second edge position measuring methods,wherein:

the first edge position measuring method estimates a position of aboundary between the second mark and the first space by comparing a timeinterval from time corresponding to a mark edge position opposite to thefirst space of the first mark in a read signal of the first recordingpattern to time corresponding to the position of the boundary betweenthe second mark and the first space in the read signal with a timeinterval of (a+i)T; and

the second edge position measuring method estimates a position of aboundary between the second mark and the second space by comparing atime interval from time corresponding to the position of the boundarybetween the second mark and the second space in a read signal of thesecond recording pattern to time corresponding to a mark edge positionopposite to the second space of the third mark in the read signal with atime interval of (b+i)T.

(2) An information recording method using a recording medium permittedto get into a first state by a first power level of an energy beam andpermitted to get into a second state by a second power level of theenergy beam higher than the first power level, for recording informationon the recording medium by moving the energy beam and the recordingmedium relatively to each other so that the recording medium isirradiated with the energy beam and the first and second states areformed on the recording medium with predetermined lengths and atpredetermined intervals, comprising the steps of:

when a period of a recording timing generating clock in a recording modeis T, and a relative velocity of the energy beam and the recordingmedium is v, forming a sequence of the second state with length avT(first mark), the first state with length ivT (first space) followingthe first mark, the second state with length mvT (second mark) followingthe first space, the first state with length jvT (second space)following the second mark and the second state with length bvT (thirdmark) following the second space as a first small recording pattern;

forming a sequence which starts with the first state and ends with thefirst state while the first and second states appear alternately by afinite number of times, as a second small recording pattern;

forming a state in which the second small recording pattern follows thefirst small recording pattern, as a basic recording pattern;

forming a state in which the basic recording patterns are repeated, as arecording pattern;

forming the recording pattern which comprises the basic recordingpatterns obtained by changing a parameter i variously while parametersa, i and m are fixed, as a first recording pattern, the parameters a, i,m and j being natural numbers;

forming the recording pattern which comprises the basic recordingpatterns obtained by changing the parameter i variously while aparameter b and the parameters i and m are fixed, as a second recordingpattern, the parameter b being a natural number;

using at least one of first and second edge position measuring methods;and

using at least one of first and second timing adjusting methods, wherein

the first edge position measuring method estimates a position of aboundary between the second mark and the first space by comparing a timeinterval from time corresponding to a mark edge position opposite to thefirst space of the first mark in a read signal of the first recordingpattern to time corresponding to the position of the boundary betweenthe second mark and the first space in the read signal with a timeinterval of (a+i)T;

the second edge position measuring method estimates a position of aboundary between the second mark and the second space by comparing atime interval from time corresponding to the position of the boundarybetween the second mark and the second space in a read signal of thesecond recording pattern to time corresponding to a mark edge positionopposite to the second space of the third mark in the read signal with atime interval of (b+i)T;

the first timing adjusting method changes timing for making the energybeam reach the second power level in accordance with a combination ofthe respective lengths of the first and second states to be formed onthe recording medium; and

the second timing adjusting method changes timing for shifting theenergy beam from the second power level to another energy level inaccordance with a combination of the respective lengths of the secondand first states to be formed on the recording medium.

(3) An information recording method using a recording medium permittedto get into a first state by a first power level of an energy beam andpermitted to get into a second state by a second power level of theenergy beam higher than the first power level, for recording informationon the recording medium by moving the energy beam and the recordingmedium relatively to each other so that the recording medium isirradiated with the energy beam and the first and second states areformed on the recording medium with predetermined lengths and atpredetermined intervals, comprising the steps of:

when a period of a recording timing generating clock in a recording modeis T, and a relative velocity of the energy beam and the recordingmedium is v, forming a sequence of the second state with length avT(first mark), the first state with length ivT (first space) followingthe first mark, the second state with length mvT (second mark) followingthe first space, the first state with length jvT (second space)following the second mark and the second state with length bvT (thirdmark) following the second space as a first small recording pattern;

forming a sequence which starts with the first state and ends with thefirst state while the first and second states appear alternately by afinite number of times, as a second small recording pattern;

forming a state in which the second small recording pattern follows thefirst small recording pattern, as a basic recording pattern;

forming a state in which the basic recording patterns are repeated, as arecording pattern;

forming the recording pattern which comprises the basic recordingpatterns obtained by changing a parameter j variously while parametersa, i and m are fixed, as a first recording pattern, the parameters a, i,m and j being natural numbers;

forming the recording pattern which comprises the basic recordingpatterns obtained by changing the parameter i variously while aparameter b and the parameters j and m are fixed, as a second recordingpattern, the parameter b being a natural number;

using at least one of first and second edge position measuring methods;

using at least one of first and second timing adjusting methods; and

using at least one of first and second timing correcting methods,wherein

the first edge position measuring method estimates a position of aboundary between the second mark and the first space by comparing a timeinterval from time corresponding to a mark edge position opposite to thefirst space of the first mark in a read signal of the first recordingpattern to time corresponding to the position of the boundary betweenthe second mark and the first space in the read signal with a timeinterval of (a+i)T;

the second edge position measuring method estimates a position of aboundary between the second mark and the second space by comparing atime interval from time corresponding to the position of the boundarybetween the second mark and the second space in a read signal of thesecond recording pattern to time corresponding to a mark edge positionopposite to the second space of the third mark in the read signal with atime interval of (b+i)T;

the first timing adjusting method changes timing for making the energybeam reach the second power level in accordance with a combination ofthe respective lengths of the first and second states to be formed onthe recording medium;

the second timing adjusting method changes timing for shifting theenergy beam from the second power level to another energy level inaccordance with a combination of the respective lengths of the secondand first states to be formed on the recording medium;

the first timing correcting method adjusts the timing in the firsttiming adjusting method based on a result of the first edge positionmeasuring method; and

the second timing correcting method adjusts the timing in the secondtiming adjusting method based on a result of the second edge positionmeasuring method.

(4) An information recording method using a recording medium permittedto get into a first state by a first power level of an energy beam andpermitted to get into a second state by a second power level of theenergy beam higher than the first power level, for recording informationon the recording medium by moving the energy beam and the recordingmedium relatively to each other so that the recording medium isirradiated with the energy beam and the first and second states areformed on the recording medium with predetermined lengths and atpredetermined intervals, comprising the steps of:

when a period of a recording timing generating clock in a recording modeis T, and a relative velocity of the energy beam and the recordingmedium is v,

forming a sequence of the second state with length avT (first mark), thefirst state with length ivT (first space) following the first mark, thesecond state with length mvT (second mark) following the first space,the first state with length jvT (second space) following the second markand the second state with length bvT (third mark) following the secondspace as a first small recording pattern;

forming a sequence which starts with the first state and ends with thefirst state while the first and second states appear alternately by afinite number of times, as a second small recording pattern;

forming a state in which the second small recording pattern follows thefirst small recording pattern, as a basic recording pattern;

forming a state in which the basic recording patterns are repeated, as arecording pattern;

forming the recording pattern which comprises the basic recordingpatterns obtained by changing a parameter i variously while parametersa, i and m are fixed, as a first recording pattern, the parameters a, i,m and j being natural numbers;

forming the recording pattern which comprises the basic recordingpatterns obtained by changing the parameter i variously while aparameter b and the parameters j and m are fixed, as a second recordingpattern, the parameter b being a natural number;

using at least one of first and second edge position measuring methods;

using at least one of first and second timing adjusting methods; and

using at least one of first and second timing correcting methods,wherein

the first edge position measuring method estimates a position of aboundary between the second mark and the first space by comparing a timeinterval from time corresponding to a mark edge position opposite to thefirst space of the first mark in a read signal of the first recordingpattern to time corresponding to the position of the boundary betweenthe second mark and the first space in the read signal with a timeinterval of (a+i)T;

the second edge position measuring method estimates a position of aboundary between the second mark and the second space by comparing atime interval from time corresponding to the position of the boundarybetween the second mark and the second space in a read signal of thesecond recording pattern to time corresponding to a mark edge positionopposite to the second space of the third mark in the read signal with atime interval of (b+i)T;

the first timing adjusting method changes timing for making the energybeam reach the second power level in accordance with a combination ofthe respective lengths of the first and second states to be formed onthe recording medium;

the second timing adjusting method changes timing for shifting theenergy beam from the second power level to another energy level inaccordance with a combination of the respective lengths of the secondand first states to be formed on the recording medium;

the first timing correcting method operates so that

in a case where the first edge position measuring method concludes thatthe time interval from the time corresponding to the mark edge positionopposite to the first space of the first mark in the read signal of thefirst recording pattern to the time corresponding to the position of theboundary between the second mark and the first space in the read signalis loner than the time interval of (a+i)T, timing of arrival at thesecond power level for forming the second state with length mT isquickened only when the second state with length mT is to be formed soas to follow the first state with length iT by the first timingadjusting method; and

in a case where the first edge position measuring method concludes thatthe time interval from the time corresponding to the mark edge positionopposite to the first space of the first mark in the read signal of thefirst recording pattern to the time corresponding to the position of theboundary between the second mark and the first space in the read signalis shorter than the time interval of (a+i)T, the timing of arrival atthe second power level for forming the second state with length mT isdelayed only when the second state with length mT is to be formed so asto follow the first state with length iT by the first timing adjustingmethod, and

the second timing correcting method operates so that

in a case where the second edge position measuring method concludes thatthe time interval from the time corresponding to the position of theboundary between the second mark and the second space in the read signalof the second recording pattern to the time corresponding to the markedge position opposite to the second space of the third mark in the readsignal is loner than the time interval of (b+j)T, timing of shiftingfrom the second power level to another energy level for forming thesecond state with length mT is delayed only when the first state withlength jT is to be formed so as to follow the second state with lengthmT by the second timing adjusting method; and

in a case where the second edge position measuring method concludes thatthe time interval from the time corresponding to the position of theboundary between the second mark and the second space in the read signalof the second recording pattern to the time corresponding to the markedge position opposite to the second space of the third mark in the readsignal is shorter than the time interval of (b+j)T, the timing ofshifting from the second power level to another energy level for formingthe second state with length mT is quickened only when the first statewith length jT is to be formed so as to follow the second state withlength mT by the second timing adjusting method.

(5) A recording medium permitted to get into a first state by a firstpower level of an energy beam and permitted to get into a second stateby a second power level of the energy beam higher than the first powerlevel, wherein

at least one of information of timing for making the energy beam toreach the second power level and information of timing for shifting thepower level from the second power level into another energy level bothof which are determined using the information recording method describedin (3) is recorded as not-rewritable information on the informationrecording medium.

(6) A recording medium permitted to get into a first state by a firstpower level of an energy beam and permitted to get into a second stateby a second power level of the energy beam higher than the first powerlevel, wherein

at least one of information of timing for making the energy beam toreach the second power level and information of timing for shifting thepower level from the second power level into another energy level bothof which are determined using the information recording method describedin (4) is recorded as not-rewritable information on the informationrecording medium.

(7) An information recording apparatus comprising:

an energy beam generator for generating an energy beam;

a power adjusting mechanism for setting a power level of the energy beamto a first power level and a second power level which is higher than thefirst power level;

a holding mechanism for holding a recording medium permitted to get intoa first state by the first power level and permitted to get into asecond state by the second power level;

a moving mechanism for moving the energy beam and the recording mediumrelatively to each other;

a positioning mechanism for irradiating a predetermined place of therecording medium with the energy beam; and

a signal processing circuit for changing information to be recorded,into the power levels of the energy beam, wherein

the information recording apparatus uses the information recordingmedium described in (5) or (6), and

the apparatus further comprises:

means for reading the not-rewritable information recorded on theinformation recording medium to thereby decode at least one of theinformation of timing for making the energy beam to reach the secondpower level and the information of timing for shifting the power levelfrom the second power level into another energy level; and

means for modulating energy pulses in accordance with the decodedinformation of timing when the second states is formed on the recordingmedium.

(8) An information recording apparatus comprising:

an energy beam generator for generating an energy beam;

a power adjusting mechanism for setting a power level of the energy beamto a first power level and a second power level which is higher than thefirst power level;

a holding mechanism for holding a recording medium permitted to get intoa first state by the first power level and permitted to get into asecond state by the second power level;

a moving mechanism for moving the energy beam and the recording mediumrelatively to each other;

a positioning mechanism for irradiating a predetermined place of therecording medium with the energy beam; and

a signal processing circuit for changing information to be recorded,into the power levels of the energy beam; and

means for executing at least one of the first and second timingcorrecting methods described in (3) or at least one of the first andsecond timing correcting methods described in (4).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a specific example of a time modulationprocedure (write strategy) of an irradiation amount of an energy beamaccording to the present invention;

FIG. 2 is a block diagram of an information recording apparatusaccording to the present invention;

FIG. 3 is a graph showing an example of experimental results of areproductive signal amplitude versus values of Peak Power;

FIGS. 4A-4C are graphs showing examples of experimental results ofreproductive signal jitter versus values of Bias Power;

FIGS. 5A-5B are views for explaining mark strings to be recorded on arecording medium;

FIGS. 6A-6B are views for explaining a reproductive signal;

FIGS. 7A-7B are views showing specific examples of a basic recordingpattern;

FIG. 8 is a view showing a specific example of a recording pattern (inwhich each mark is 6vT long);

FIG. 9 is a view showing a specific example of a recording pattern (inwhich each mark is 5vT long);

FIG. 10 is a view showing a specific example of a recording pattern (inwhich each mark is 4vT long); and

FIG. 11 is a view showing a specific example of a recording pattern (inwhich each mark is 3vT long).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described below in detail on the basis ofthe following embodiments.

(First Embodiment)

Referring first to FIG. 1, there is shown an example of the change of apower level of an energy beam, which is irradiated on the recordingmedium when information is recorded thereon, with the passage of time.The way of changing the power level with the passage of time in therecording of information will be hereinafter referred to as “writestrategy” or “recording strategy”. The write or recording strategy willbe described with respect to DVD-RAM as an example.

In the case of DVD-RAM, each of the shortest mark and the shortest spaceis 3T long (three times as long as T) when T is a time interval of areference clock pulse signal for recording/reproducing. Further, each ofthe largest mark and the largest space is generally 11T long. As aspecial pattern, 14T-long mark and space may be provided.

When an NRZI signal is given as information to be recordedtime-sequentially on a recording medium, the NRZI signal is convertedinto a time-sequential change of the power level of the energy beam by asuitable signal processing circuit. FIG. 1 shows the time-sequentialchange of the power level as waveforms of light pulses.

The power levels are set to four values, Peak Power, Bias Power 1, BiasPower 2 and Bias Power 3. The recording medium is permitted to get intoa first state by Bias Power 1 (first power level) and is permitted toget into a second state by Bias Power 2 (second power level). Bias Power3 (third power level) is equal to or less than Bias Power 1. When aregion of the second state is formed on the recording medium and thelength of the region is 4T or more (that is, the length of the NRZIsignal is 4T or more), the energy beam is multi-pulsated by mixing thepower level period of Bias Power 3 into the irradiation period of PeakPower. In the multi-pulsated energy beam, the first light pulse and thelast light pulse will be referred to as “a first pulse” and “a lastpulse”, respectively. A light pulse reciprocating between Peak Power andBias Power 3 is repeated in accordance with the length of the NRZIsignal so that the repeated light pulses are disposed between the firstpulse and the last pulse. The number of the repetitions is (n−4) whenthe length of the NRZI signal is nT (n>3). Each of the repeated pulsesput between the first pulse and the last pulse is called “a comb-likepulse”. That is, when the region of the second state correspondingly tothe NRZI signal with length 5T is formed or more, the recording pulsesignal is composed of the first pulse, the comb-like pulse and the lastpulse. When the region of the second state corresponding to the NRZIsignal with length 4T is formed, the recording pulse signal is composedof the first pulse and the last pulse. When the region of the secondstate corresponding to the NRZI signal with length 3T is formed, therecording pulse signal is composed of a single light pulse.

Bias Power 2 (fourth power level) set to be equal to or less than BiasPower 1 is used as follows. For the NRZI signal with the length equal toor more than 4T, the power level following the last pulse is kept inBias Power 2 for a predetermined time. For the NRZI signal with length3T, the power level following the single light pulse is kept in BiasPower 2 for a predetermined time.

There is a possibility that the power level of Bias Power 1 may be equalto that of Bias Power 2 or Bias Power 3. There is also a possibilitythat all the power levels of Bias Power 1, Bias Power 2 and Bias Power 3may be the same. Reference values of Peak Power, Bias Power 1, BiasPower 2 and Bias Power 3 may be recorded, as medium information, in asuitable place on the recording medium in advance. A portion on therecording medium used to record the medium information concerning therecording strategy is called “a control data zone information track”.The reference values of the power levels are read from the control datazone information track on the recording medium, and then the respectivepower levels in the writing mode are determined on the basis of the readreference values.

The definition of the recording waveform will be first described in thecase where the region of the second state corresponding to the NRZIsignal with the length equal to or more than 4T is formed on therecording medium. The leading edge of the first pulse of the write pulsestring is defined by time after the passage of T_(SFP) from the leadingedge of the NRZI signal. The trailing edge of the first pulse of thewrite pulse string is defined by time after the passage of T_(EFP) fromthe leading edge of the NRZI signal. The length of the first pulse isT_(FP). The value of T_(FP) is equal to a value obtained by subtractingT_(SFP) from T_(EFP). The leading edge of the last pulse of the writepulse string is defined by reference to time preceding the trailing edgeof the NRZI signal by time 2T. The last pulse rises at time when timeT_(SLP) is passed after the reference time. The trailing edge of thelast pulse of the write pulse string is also defined by reference to thetime preceding the trailing edge of the NRZI signal by time 2T. The lastpulse falls at time when time T_(ELP) is passed after the referencetime. The length of the last pulse is T_(LP). The value of T_(LP) isequal to a value obtained by subtracting T_(SLP) from T_(ELP).

The comb-like pulse string may be disposed between the first pulse andthe last pulse. The leading edge of each comb-like pulse in thecomb-like pulse string coincides with a reference clock position. Eachcomb-like pulse falls at time when time T_(MP) is passed after theleading edge thereof.

The definition of the recording waveform will be described in the casewhere the region of the second state corresponding to the NRZI signalwith length 3T is formed on the recording medium. The leading edge ofthe light pulse is present at time when T_(SFP) is passed after theleading edge of the NRZI signal. The trailing edge of the light pulse isdefined by reference to time preceding the tailing edge of the NRZIsignal by time 2T. The trailing edge of the light pulse is present attime when time T_(ELP) is passed after the reference time.

A portion having the power level of Bias Power 2 follows the last pulsein the case of the NRZI signal with the length equal to or more than 4T,or the recording pulse in the case of the NRZI signal with length 3T.The length of the portion is T_(LC). The values of T_(SFP), T_(EFP),T_(FP), T_(SLP), T_(ELP), T_(LP), T_(LC) and T_(MP) for defining therecording pulse are determined on the basis of the reference valueswhich are read from the control data zone information track of therecording medium.

The values of T_(SFP), T_(EFP), T_(FP), T_(SLP), T_(ELP), T_(LP), T_(LC)and T_(MP) for defining the recording pulse are not always constant butmay be required to be changed in accordance with the combination of theNRZI signals. Particularly, when the case of the DVD-RAM with therecording capacity of 4.7 GB per side is taken as an example, length 3Tof the shortest mark is about 0.42 μm which is shorter than the writespot radius 0.45 μm. When such a high-density recording is performed,the thermal interference between adjacent marks may become large, sothat it is difficult to perform the stable recording continuously.Therefore, it is thought of that the recording waveform is changedadaptively in accordance with the combination of the front and rear ofthe NRZI signal. There are the following two methods for correcting theshifting of the front edge.

(1) A method of changing T_(SFP) while fixing T_(EFP). On this occasion,T_(FP) changes with the change of T_(SFP).

(2) A method of changing T_(SFP) while fixing T_(FP). On this occasion,T_(EFP) changes with the change of T_(SFP).

There are the following two methods for correcting the shifting of therear edge.

(1) A method of changing T_(ELP) while fixing T_(SLP). On this occasion,T_(LP) changes with the change of T_(ELP).

(2) A method of changing T_(ELP) while fixing T_(LP). On this occasion,T_(SLP) changes with the change of T_(ELP).

The selection of the aforementioned methods for controlling the shiftingof the front and rear edges depends on the way of designing therecording medium and the recording characteristic of the recordingmedium. As the recording medium producer knows best which method is tobe selected for controlling the shifting of the front and rear edges,the recording medium producer can recommend the selection of the edgeshifting control method for the information recording apparatus. Thatis, the recording medium producer writes information concerning therecommended edge shifting control method in a specific place on therecording medium, so that the information recording apparatus can readthe recommendatory information to determine the edge shifting controlmethod. In this case, the information recording apparatus can usethoroughly the medium characteristic intended by the recording mediumproducer, so that the information recording can be performed moststably. Further, the recording medium producer can prepare a look-uptable for the edge shifting control and record the look-up table on therecording medium. The information recording apparatus reads the look-uptable and then performs the edge shifting control on the basis of thelook-up table. In this manner, the information recording apparatus canuse thoroughly the medium characteristic intended by the recordingmedium producer, so that the information recording can be performed moststably. The aforementioned idea makes it possible to provide means ofachieving the best recording compatibility while keeping thehigh-density recording.

When the length of the mark to be recorded at present is M(n) and thelength of the space preceding the mark is S(n−1), the look-up tableconcerning the front edge contains the arrangement of values determinedby the combinations of M(n) and S(n−1). This value may take a positivevalue or a negative value.

When the length of the mark to be recorded at present is M(n) and thelength of the space following the mark is S(n+1), the look-up tableconcerning the rear edge contains the arrangement of values determinedby the combinations of M(n) and S(n+1). This value also may take apositive value or a negative value.

When T_(SFP) and T_(ELP) are changed in accordance with the combinationsof the front and rear edges of the NRZI signal as described above, themark edge position can be controlled always accurately.

Although the use of the write strategy having four power levels in therecording mode makes it possible to form the marks stably, this iseffective when the power levels are set appropriately. It is practicablebut complex in procedure to find the optimum combination of the fourpower levels as four independent variables. Furthermore, there is apossibility that the large number of steps are required for achievingthe optimum combination. Therefore, it is thought of that the four powerlevels are classified into groups and the groups are assignedindependent variables to thereby make it possible to reduce the numberof independent variables to thereby simplify the procedure of findingthe optimum combination of independent variables.

In the case of the phase-change recording medium such as a DVD-RAM, ithas been found from a process of elucidating the recording mechanism byexamination that there are considerably high correlation among thelevels of Bias Power 1, Bias Power 2 and Bias Power 3. Assume now thatPeak Power is assigned to a first group and Bias Power 1, Bias Power 2and Bias Power 3 are assigned to a second group. An independent variableassigned to the first group is called “magnification factor x(hereinafter merely referred to as “x”)”. An independent variableassigned to the second group is called “magnification factor y(hereinafter merely referred to as “y”)”. The initial value of PeakPower is multiplied by x to obtain the value of Peak Power in therecording mode. The initial values of Bias Power 1, Bias Power 2 andBias Power 3 are multiplied by y to obtain the values of Bias Power 1,Bias Power 2 and Bias Power 3 in the recording mode. Information isrecorded while x and y are changed variously and the recordedinformation is reproduced. The fluctuation (reproductive jitter) of areproductive signal is measured. The values of x and y are adjusted sothat the measured reproductive jitter is not larger than a predeterminedvalue. In this manner, the number of the independent variables can bereduced from four to two, so that the procedure of finding the optimumcombination of the independent variables can be simplified. Furthermore,as the procedure is simplified, the reliability on finding the optimumcombination can be improved.

Another classification may be thought of. Particularly, the procedurecan be simplified when the four power levels are collected into onegroup. That is, the initial value of Peak Power is multiplied by z toobtain the value of Peak Power in the recording mode, and the initialvalues of Bias Power 1, Bias Power 2 and Bias Power 3 are multiplied byz to obtain the values of Bias Power 1, Bias Power 2 and Bias Power 3 inthe recording mode. Information is recorded while the magnificationfactor z (hereinafter merely referred to as “z”) is changed variouslyand the recorded information is reproduced. The fluctuation of areproductive signal (reproductive jitter) is measured. The value of z isadjusted so that the measured reproductive jitter is not larger than apredetermined value. In this manner, the number of the independentvariables can be reduced from four to one, so that the procedure offinding the optimum combination of the independent variables can besimplified more greatly. Furthermore, as the procedure is simplifiedmore greatly, the reliability on finding the optimum combination can beimproved more greatly.

It is thought of that the initial values of Peak Power, Bias Power 1,Bias Power 2 and Bias Power 3 are determined on the basis of therecommended values which are read from the control data zone informationtrack of the recording medium. In this case, the power levels can beoptimized while the power balance in each group is kept on the basis ofthe values recommended by the recording medium maker. Accordingly, thereis obtained a technical effect that the optimum power levels for theinformation recording can be determined while the compatibility is keptbetter.

As the method of assigning Peak Power to the first group and assigningBias Power 1, Bias Power 2 and Bias Power 3 to the second group toobtain the optimum values of x and y, there is a method in which theoptimum values of x and y are obtained on the basis of the value of thereproductive jitter which is obtained in accordance with the combinationof the values of x and y while x and y are changed at random. However, amethod in which the optimum values of x and y are obtained while x and yare changed systematically may be rather excellent to obtain the optimumvalues accurately.

As a simplest method, there is the following method. The values of x andy are quantized at suitable step intervals in a range between themaximum value and the minimum value. The values of the reproductivejitter are obtained in accordance with all of the combinations of thevalues of x and y. The combination of the values of x and y with whichthe obtained value of the reproductive jitter is not larger than apredetermined value is obtained. This method requires a considerabledeal of time because the number of the measurement times of thereproductive jitter is large, but has a technical effect that theoptimum values of x and y can be obtained securely.

As another method for obtaining the optimum values of x and y, there isa method in which the following first, second and third procedures arecarried out successively.

(1) First Procedure

The value of y is set to be “1”. Value x1 of x to minimize thereproductive jitter is obtained while x is changed at intervals ofsuitable step width dx in a range of from the lower limit xs of x to theupper limit xm of x. For example, when the lower limit xs, the upperlimit xm and the step width dx are 0.85, 1.15 and 0.05, respectively,the value x1 of x to minimize the reproductive jitter is obtained byobtaining the value of the reproductive jitter corresponding to eachvalue of x while changing x to 0.85, 0.9, 0.95, 1.0, 1.05, 1.1 and 1.15.Further, value x2 of x to make the value of the reproductive jitterequal to value a is obtained. The obtained value x2 is multiplied by cto obtain value x3. As a specific example, data of the values of thereproductive jitter obtained with the change of x are used. The value x2of x to make the value of the reproductive jitter equal to the value ais obtained by the linear interpolation on the basis of two adjacentvalues of x when one of the values of the reproductive jittercorresponding to the two adjacent values of x is larger than the value aand the other is smaller than the value a. When there is no data to bepicked for the linear interpolation, the upper limit xm and/or the lowerlimit xs may be widened to take data of the values of the reproductivejitter in a wider range or the value x2 may be predicted by use of theexisting data. Finally, the value x1 and the value x3 are compared witheach other, so that smaller one is obtained as value x4.

When the minimum point of the reproductive jitter is to be obtained, itmay be difficult to find the minimum point of the reproductive jitterbecause the reproductive jitter little changes though the value of xchanges near the optimum value of x. In this case, the following methodmay be used as a substitute for the method of finding the minimum pointof the reproductive jitter. As a curve of the reproductive jitter forthe value of x is depicted as a parabolic curve, two values of x aregenerally present as the value of x to make the value of thereproductive jitter equal to the value a. Accordingly, smaller one x1Land larger one x1H of the values of x to make the value of thereproductive jitter equal to the value a are obtained. Then, anarithmetical mean of the values x1L and x1H is obtained as the value x1.However, in order to find the value x1L, it is necessary to increase thevalue of x to a considerably large value. Accordingly, there is apossibility that the value of x may be restricted by the upper limit ofx. Accordingly, in this case, it is difficult to apply the method usingthe values X1L and X1H.

(2) Second Procedure

The value of x is set to be x4. Value y1 of y to minimize thereproductive jitter is obtained while y is changed at intervals ofsuitable step width dy in a range of from the lower limit ys of y to theupper limit ym of y. For example, when the lower limit ys, the upperlimit ym and the step width dy are 0.85, 1.15 and 0.05, respectively,the value y1 of y to minimize the reproductive jitter is obtained byobtaining the value of the reproductive jitter corresponding to eachvalue of y while changing y to 0.85, 0.9, 0.95, 1.0, 1.05, 1.1 and 1.15.When the minimum point of the reproductive jitter is to be obtained, itmay be difficult to find the minimum point of the reproductive jitterbecause reproductive jitter little changes though the value of y changesnear the optimum value of y. In this case, the following method may beused as a substitute for the method of finding the minimum point of thereproductive jitter. As a curve of the reproductive jitter for the valueof y is depicted as a parabolic curve, two values of y are generallypresent as the value of y to make the value of the reproductive jitterequal to the value a. Accordingly, smaller one y1L and larger one y1H ofthe values of y to make the value of the reproductive jitter equal tothe value a are obtained. Then, an arithmetical mean of the values y1Land y1H is obtained as the value y1. Either of the aforementionedmethods may be used. The value of y obtained by either of theaforementioned methods may be used as the final value y1.

(3) Third Procedure

The value of y is set to be y1. Value x5 of x to minimize thereproductive jitter is obtained while x is changed at intervals of thesuitable step width dx in a range of from the lower limit xs of x to theupper limit xm of x in the same manner as in the first procedure.Further, value x6 of x to make the value of the reproductive jitterequal to the value a is obtained. The obtained value x6 is multiplied byc to obtain value x7 in the same manner as in the first procedure.Finally, the value x5 and the value x7 are compared with each other, sothat smaller one is obtained as value x8. When the minimum point of thereproductive jitter is to be obtained, it may be difficult to find theminimum point of the reproductive jitter because the reproductive jitterlittle changes though the value of x changes near the optimum value ofx. Also in this case, the minimum point of the reproductive jitter maybe found in the same manner as in the substitutive method (using thevalues x1L and x1H) described above in the first procedure.

At time when the aforementioned first, second and third procedures arecompleted, the optimum values of x and y are judged to be x8 and y1,respectively. In the method using the first, second and third proceduressuccessively to obtain the optimum values of x and y, there is atechnical effect that the optimum values of x and y are obtained by theminimum number of time of the jitter measurements.

An information recording apparatus according to the first embodiment ofthe present invention will be described below with reference to FIG. 2.FIG. 2 is a block diagram of the information recording apparatusaccording to the first embodiment of the present invention. Forconvenience' sake of description, FIG. 2 shows the case where arecording medium 100 is mounted on the information recording apparatus.The recording medium 100 is essential for storage of information. Therecording medium 100 can be detached from the information recordingapparatus or attached onto the information recording apparatus asoccasion demands.

Referring to FIG. 2, a disk clamping mechanism 112 is attached to arotation shaft 111 of a motor 110 which is attached to a box 108. Thedisk clamping mechanism 112 holds the recording medium 100. That is, thedisk clamping mechanism 112 serves as a mechanism for holding therecording medium 100. Further, the motor 110, the rotation shaft 111 andthe disk clamping mechanism 112 constitute a moving mechanism for movingthe recording medium 100 and the energy beam relatively.

A rail 115 is attached to the box 108. Rail guides 116 guided by therail 115 are attached to a casing 117. A linear gear 119 is alsoattached to the casing 117. A rotary gear 120 is attached to the lineargear 119. The rotation of a rotating motor 118 attached to the box 108is transmitted to the rotary gear 120 to thereby move the casing 117linearly along the rail 115. The direction of the linear motionsubstantially coincides with the direction of the radius of therecording medium 100.

Magnets 121 are attached to the casing 117. An objective lens 136 isalso attached to the casing 117 through suspensions 123. The suspensions123 can move the objective lens 136 both in the direction substantiallyequal to the direction of the normal to the recording surface of therecording medium 100 and in the direction substantially equal to thedirection of the radius of the recording medium 100. Coils 122 areattached to the objective lens 136 so as to be substantially opposite tothe magnets 121, respectively. The objective lens 136 can be moved bothin the direction substantially equal to the direction of the normal tothe recording surface of the recording medium 100 and in the directionsubstantially equal to the direction of the radius of the recordingmedium 100 by magnetic force generated when electric current is suppliedto the coils 122. The rail 115, the rail guides 116, the casing 117, themagnets 121, the suspensions 123, the coils 122 and the objective lens136 constitute a positioning mechanism for irradiating a predeterminedplace of the recording medium 100 with an energy beam.

A semiconductor laser 131 which serves as an energy beam generator isattached to the casing 117. The energy beam emitted from thesemiconductor laser 131 passes through both a collimating lens 132 and abeam splitter 133 and then passes through the objective lens 136. A partof light passed through the objective lens 136 is reflected by therecording medium 100 and then passes through the objective lens 136 soas to enter the beam splitter 133. A part of the light is reflectedtoward a detection lens 134 by the beam splitter 133, converged by thedetection lens 134 and then enters a photo detector 135. As a result,the light intensity thereof is detected. The photo detector 135 isdivided into a plurality of light-receiving areas. Light intensitydetected by each light-receiving area is amplified and calculated by anamplifier 152 so that information (a servo signal) of the relativepositional relation between a light spot converged by the objective lens136 and the recording medium 100 and an information read signal aredetected. The servo signal is sent to a servo controller 151. The readsignal is sent to a slicer 170 and two-valued by the slicer 170. Thetwo-valued signal is sent both to a decoder 153 and to a time intervalmeasuring circuit 171.

When the recording medium 100 is mounted on the information recordingapparatus and fixed by the disk clamping mechanism 112, a detector 140operates to send its output signal to a system controller 150. Thesystem controller 150 controls the motor 110 on the basis of the outputsignal of the detector 140 to rotate the recording medium 100 at anappropriate rotational speed. Further, the system controller 150controls the rotating motor 118 to position the casing 117 in anappropriate position. Further, the system controller 150 makes thesemiconductor laser 131 emit light. At the same time, the systemcontroller 150 operates the servo controller 151 to operate the rotatingmotor 118 and supply electric current to the coils 123 so that the focalspot formed by the objective lens 136 is positioned in a predeterminedplace of the recording medium 100. Then, the servo controller 151 sendsa signal to the system controller 150 so as to inform it of the factthat the focal spot is formed in the recording medium 100. The systemcontroller 150 gives an instruction to the decoder 153 to decode theread signal. When the read track is not the control data zoneinformation track, the system controller 150 gives an instruction to theservo controller 151 so that the focal spot is positioned on the controldata zone information track. On the basis of the aforementionedoperation, the system controller 150 reads the medium informationconcerning the recording from the control data zone information track.

Information concerning the recording strategy described above withreference to FIG. 1 is written in the control data zone informationtrack in advance. The system controller 150 reads parameters of therecording strategy from the recording medium 100 to specify informationsuch as the recording power levels, time-relations among the recordingpulses, the look-up tables, the recommended adaptive control methods andso on. The system controller 150 writes these parameters of therecording strategy in a parameter table of the signal processing circuit154, a parameter table of a delay circuit 155 and current sink amountparameter tables of current sinks 156. By the selection of the adaptivecontrol method, the way of writing parameters in the parameter table ofthe delay circuit 155 is changed or a switch of the delay circuit 155 ischanged, so that the operation of each adaptive control method describedabove with reference to FIG. 1 is achieved.

Only when the recording medium 100 is write-enabled, the systemcontroller 150 may read the parameters of the recording strategy of therecording medium 100 and then write these in the parameter table of thesignal processing circuit 154, the parameter table of the delay circuit155 and the current sink amount parameter tables of the current sinks156. For example, when the recording medium 100 is write-disabledbecause a write protection switch provided in the casing of therecording medium 100 and so forth is selected in a write-disabledposition or a high-order controller of the information recordingapparatus instructs write-disable, a series of operations such as thereading of the recording strategy parameters or the like can be omitted.A detection switch 141 is attached to the box 108 in order to detect thewrite protection switch. An output signal of the detection switch 141 issent to the system controller 150. In the write-disabled state, theoperation of reading the recording strategy parameters can be stopped toshorten the readiness time for making the recording medium 100read-enabled after the fixation of the recording medium 100 by the diskclamping-mechanism 112.

When an instruction to reproduce information is given from thehigh-order controller through an input connector 159, the systemcontroller 150 instructs the servo controller 151 to position the focalspot in a suitable place of the recording medium 100. After a signalobtained in the photo detector 135 is decoded by the slicer 170 and thedecoder 153, information read through an output connector 158 is sent tothe high-order controller.

When an instruction to write information as well as information to bewritten is given from the high-order controller through the inputconnector 159, the system controller 150 instructs the servo controller151 to position the focal spot in a suitable place of the recordingmedium 100. The information to be written is converted into an NRZIsignal by a signal processing circuit 161. The NRZI signal is convertedinto a string of suitable pulses by the signal processing circuit 154.The pulse string is sent to the current sinks 156 through the delaycircuit 155. The signal processing circuits 161 and 154 constitute asignal processing circuit by which the information to be written isconverted into a recording pulse string (that is, power levels of theenergy beam).

A constant-current source 157 is connected to the semiconductor laser131 so that the total current consumed by the semiconductor laser 131and the current sinks 156 is kept constant. The plurality of currentsinks 156 are connected to the constant-current source 157. It dependson the pulse string generated by the signal processing circuit 154 andthen passed through the delay circuit 155 whether the current sinks 156operate to absorb current or not. By the operation of the current sinks156, a part of current output from the constant-current source 157 isabsorbed to the current sinks 156, so that the amount of current flowinginto the semiconductor laser 131 is reduced. Accordingly, the energylevel of the energy beam emitted from the semiconductor laser 131 ischanged. When the plurality of current sinks 156 are operated insuitable timing, the signal processing circuit 154 and the delay circuit155 achieve the recording strategy shown in FIG. 1.

In order to carry out the aforementioned operation, the informationrecording apparatus is supplied with electric power through a terminal160 from the outside.

When the necessity of writing information occurs or before informationwriting occurs, the power level of the energy beam for writinginformation may be optimized or updated. In this case, the systemcontroller 150 sends a suitable recording pattern to the signalprocessing circuit 154 to form a string of recording marks on therecording medium 100. Then, a reproductive signal obtained byreproduction of the recording mark string is two-valued by the slicer170 and then sent to the time interval measuring circuit 171. The timeinterval measuring circuit 171 measures the fluctuation (jitter) of thereproductive signal and sends the measured result to the systemcontroller 150. The system controller 150 changes the recording powerlevels on the basis of the measured result of the fluctuation (jitter)and according to the procedures described above with reference toFIG. 1. The system controller 150 sends the suitable recording patternto the signal processing circuit 154 again to form the recording markstring on the recording medium 100 using the new recording power levels.In this manner, when the measurement of the reproductive jitter as wellas the updating of the recording power levels is repeated by thenecessary number of times, the optimum recording power levels forwriting information in the given recording medium 100 can be generatedas occasion demands. Accordingly, there is a technical effect thatinformation can be always written on the recording medium 100 stably andreliably.

Incidentally, there is a circuit having a time interval analyzer (TIA)function as an example of the time interval measuring circuit 171. Asanother example of the time interval measuring circuit 171, there is amethod in which PLL (Phase-Locked Loop) is applied to a digital signaltwo-valued by the slicer 170 and the magnitude of an error signal in thePLL (the amount of mismatch between the edge position of a clock signalgenerated in the PLL and the edge position of the two-valued digitalsignal) is regarded as the jitter amount of the two-valued digitalsignal. A PLL circuit is essential when the reproductive signal isdecoded by the decoder 153. Accordingly, the use of the PLL error signalhas a technical effect that it is unnecessary to implement theinformation recording apparatus with a new TIA specially. As a furtherexample of the time interval measuring circuit 171, there is a method inwhich the digital signal two-valued by the slicer 170 is compared withthe recording pattern given to the signal processing circuit 154 in thewriting mode and the frequency of error pulses obtained from the amountof mismatches in the comparison is regarded as the jitter amount of thetwo-valued digital signal. In this case, there is a technical effectthat the jitter amount of the two-valued digital signal can be evaluatedwithout providing any new circuit in the information recording apparatusspecially.

As described above, according to the present invention, the recordingmark edges can be always positioned in the predetermined points stablyeven in the case where the high-density recording in which the shortestrecording mark length is not larger than the radius of the recordingspot is performed. Accordingly, there is a technical effect thatinformation can be always recorded in the recording medium stably andreliably.

(Second Embodiment)

An information recording method according to a second embodiment of thepresent invention will be described below with reference to FIG. 1.

As described above, it is thought of that the initial values of PeakPower, Bias Power 1, Bias Power 2 and Bias Power 3 are determined on thebasis of the recommended values which are read from the control datazone information track of the recording medium.

Assume now that the recording medium, the recording power levels for therecording medium and the look-up tables for the edge shifting are givento the information recording apparatus. The values of the recordingpower levels and look-up tables may be those which are read from apredetermined place of the recording medium, or may be obtained by somemethod in the information recording apparatus. The information recordingapparatus performs the recording using the recording power levels andthe look-up tables. However, the given recording power levels and thegiven look-up tables do not always indicate the optimum values for thecombination of the present recording characteristic of the informationrecording apparatus and the recording medium. Because the recordingcharacteristic of the information recording apparatus may change withthe change of the environmental temperature in use and with the passageof time or there may be the variation of the recording characteristicamong the information recording apparatuses. That is, here is consideredthe case where a problem of compatibility occurs in the recording powerlevels and the look-up tables because of the change of characteristicwith the passage of time, the individual difference in thecharacteristic of the information recording apparatus, and so on.

In a conventional phase-change recording medium, only the optimizationof the recording power levels needs to be considered when there is nolook-up table for the edge shifting in the recording mode. When theDVD-RAM with the capacity of 2.6 GB per side is taken as an example, theoptimum recording power levels are generally set by the followingprocedure though there are various methods for setting the recordingpower levels depending on the information recording apparatuses.

(1) While Bias Power 1 (named by Standard Book for DVD-RAM with acapacity of 2.6 GB per side) and Bias Power 2 (named by Standard Bookfor DVD-RAM with a capacity of 2.6 GB per side) are fixed but Peak Power(named by Standard Book for DVD-RAM with a capacity of 2.6 GB per side)is changed, a random pattern is recorded and then reproduced to measurethe jitter of the productive signal. A recording power level which is1.2 times as much as the recording power level to make the value of thejitter equal to 13% is set as Peak Power (named by Standard Book forDVD-RAM with a capacity of 2.6 GB per side).

(2) While Bias Power 1 (named by Standard Book for DVD-RAM with acapacity of 2.6 GB per side) is changed, a random pattern is recordedand then reproduced to measure the jitter of the reproductive signal.The bias power level to minimize the value of the jitter is set as BiasPower 1 (named by Standard Book for DVD-RAM with a capacity of 2.6 GBper side). Alternatively, a bias power level at the midpoint of twopoints at each of which the value of the jitter is equal to 13% is setas Bias Power 1 (named by Standard Book for DVD-RAM with a capacity of2.6 GB per side).

(3) As occasion demands, the steps (1) and (2) are retried.

That is, the optimum recording power levels are obtained on the basis ofthe curve of the jitter of the reproductive signal which is obtained byrecording and then reproducing the random pattern.

When the higher-density recording than the DVD-RAM with a capacity of2.6 GB per side is performed by use of the edge-shifting look-up tableswhich are absent in the DVD-RAM with a capacity of 2.6 GB per side, itmay be impossible to set the power levels sufficiently accurately on thebasis of the aforementioned measurement of the reproductive jitter ofthe random pattern. That is, the edge-shifting look-up tables per se maybe out of compatibility. In this case, the aforementioned reproductivejitter of the random pattern takes a value worse than that is expectedbecause the look-up tables are unsuitable, so that the power levelscannot be determined normally. In this case, it may be preferable thatthe power levels are set without using the look-up tables which havebeen already out of compatibility.

The inventor(s) of the present application has examined the way ofupdating the recording power levels and the look-up tables in the casewhere the recording power levels and the look-up tables are out ofcompatibility as described above. Conclusively, it is recognized thatthe recording power levels and the look-up tables can be updatedaccurately when the following procedure is carried out in theinformation recording apparatus using the phase-change medium having thehigher surface density than the DVD-RAM with a capacity of 2.6 GB perside and performing the recording control using the look-up tables.

(1) Peak Power and Bias Power are set on the basis of a repetitionpattern of mark and space having the same length. Peak Power and BiasPower thus set are called temporary Peak Power and temporary Bias Power,respectively. A sequence for determining the power levels and arecording pattern are of importance. Incidentally, the terminology “BiasPower” used herein contains Bias Power 1, Bias Power 2 and Bias Power 3shown in FIG. 1.

(2) The look-up tables are optimized using the temporary Peak Power andthe temporary Bias Power.

(3) Peak Power and Bias Power are set on the basis of a random patternusing the optimized look-up tables. A sequence for determining the powerlevels and the recording pattern are of importance.

Although there are various methods for setting Peak Power and Bias Powerspecifically in the step (1), a method convenient to the informationrecording apparatus may be selected. It is important that the sequencefor setting the power levels (a sequence in which Peak Power isoptimized while Bias Power is fixed to an optimum value after Bias Poweris optimized while Peak Power is fixed to its initial value) and therepetition pattern of mark and space having the same length are used.The necessity of the sequence will be described below.

FIG. 3 shows an experimental example for determining Peak Power. Theexperiment is made under the condition of the DVD-RAM with a capacity of4.7 GB per side. The abscissa axis shows Peak Power. The amplitude ofthe reproductive signal of the repetition pattern of mark with length 3Tand space with length 3T is plotted on Peak Power. Bias Power 1 is usedas a parameter. When Bias Power 1 is to be changed, Bias Power 2 andBias Power 3 are changed so that the ratios of Bias Power 2 and BiasPower 3 to Bias Power 1 are kept constant. When Peak Power is to beobtained from this experiment, the value of Peak Power obtained when theamplitude of the reproductive signal is reduced by 3 dB from thesaturation level of the amplitude in the large value of Peak Power ismultiplied by 1.2 to obtain the optimum power level. It is obvious fromthe experimental result that the optimum value of Peak Power changes asBias Power 1 changes. That is, when a sequence in which Peak Power isfirst optimized is used for optimizing Peak Power and Bias Power, theoptimum value of Peak Power changes in accordance with the initial valueof Bias Power which is given at option for optimizing Peak Power.

FIGS. 4A-4C show experimental examples for determining Bias Power 1. Ineach of the graphs, the abscissa axis shows Bias Power 1. There areplotted a jitter curve (3T on 11T) in the case where the repetitionpattern of mark with length 3T and space with length 3T is overwrittenon the repetition pattern of mark with length 11T and space with length11T, and a jitter curve (11T on 3T) in the case where the repetitionpattern of mark with length 11T and space with length 11T is overwrittenon the repetition pattern of mark with length 3T and space with length3T. The ordinate axis shows the value of the jitter. An overlap portionof the two curves is sliced at the jitter value of about 13%, so that anaverage of the two values of Bias Power 1 at the jitter value of 13% isset as the optimum value of Bias Power 1. When Bias Power 1 is to bechanged, Bias Power 2 and Bias Power 3 are changed so that the ratios ofBias Power 2 and Bias Power 3 to Bias Power 1 are kept constant. Whenthe aforementioned optimization is performed while Peak Power ischanged, the value of Bias Power 1 which is always kept constant isobtained irrespective of the value of Peak Power. That is, when BiasPower 1 is first optimized in the case where Peak Power and Bias Power 1are optimized, the optimum value of Bias Power 1 which is always correctis obtained irrespective of the initial value of Peak Power. Further,when Peak Power is optimized after the optimization of Bias Power 1, theoptimum value of Peak Power is also obtained. As described above, notthe random pattern but the repetition pattern of mark and space havingthe same length is used in the optimization of Bias Power 1 and PeakPower. This is important to determine the power levels irrespective ofthe look-up tables which have been already out of compatibility. Whenthe aforementioned recording pattern and the aforementioned optimizingsequence are used, there is a technical effect that the recording powerlevels which are always correct can be determined.

In the step (2), the look-up tables are updated. As the temporary powerlevels are determined in the step (1), the look-up tables at the optimumpower levels can be determined. Although there are various methods fordetermining the look-up tables, the look-up tables may be determined bya method convenient to the information recording apparatus. Accordingly,the way of determining the look-up tables will be not describedhereinafter.

In the step (3), the recording power levels are determined finally. Thereason why the recording power levels are adjusted finally though thetemporary power levels and the look-up tables have been alreadydetermined in the steps (1) and (2) is that an optimum recordingcondition in a random pattern is found. As the look-up tables have beenalready updated in the step (2), the jitter in the random pattern isreduced sufficiently. Accordingly, the reproductive jitter in the randompattern is an effective means for determining the recording powerlevels. Although various procedures are used for determining the powerlevels specifically, any procedure may be selected in accordance withthe information recording apparatus. An example of the procedure will bedescribed below. While Bias Power 1 is changed in the condition thatPeak Power is set to be equal to the temporary Peak Power, a randompattern is recorded and then reproduced to measure the reproductivejitter. The bias power level to minimize the reproductive jitter is setas the optimum Bias Power 1. Alternatively, the bias power level at themidpoint of two jitter points crossing the reproductive jitter value of13% is set as the optimum Bias Power 1. Then, while Peak Power ischanged in the condition that Bias Power 1 is set to the optimum BiasPower 1, a random pattern is recorded and then reproduced to measure thereproductive jitter. A recording power level which is 1.2 times as muchas the recording power level to make the reproductive jitter value equalto 13% is set as the optimum Peak Power. As occasion demands, thesetting of Bias Power and Peak Power is repeated. A sequence foroptimizing the power levels is of importance. It is important from thesame necessity as described above that Peak Power is set after theoptimization of Bias Power 1. Although here is described “optimizationof Bias Power 1”, Bias Power 2 and Bias Power 3 are changed with thechange of Bias Power 1 while the ratios of Bias Power 2 and Bias Power 3to Bias Power 1 are kept constant.

An information recording apparatus according to the second embodiment ofthe present invention will be described below. The configuration of theinformation recording apparatus according to this embodiment is the sameas that of the information recording apparatus according to the firstembodiment of the present invention shown in FIG. 2. Accordingly, theoperation of the information recording apparatus according to thisembodiment will be described below with reference to FIG. 2.

When the necessity of writing information occurs or before theinformation writing occurs, the power level of the energy beam forwriting information may be optimized or the value of the power level maybe updated. Further, the look-up table for correcting the front edgetiming and the look-up table for correcting the rear edge timing in thewrite mode may be optimized or the table values may be updated. In thiscase, the system controller 150 sends a suitable recording pattern tothe signal processing circuit 154 to form a recording mark string on therecording medium 100. Then, the recording mark string is reproduced. Thelevel of the reproductive signal is measured by the amplifier 152, andthen the measured value is sent to the system controller 150. Further,the reproductive signal is two-valued by the slicer 170, and then sentto the time interval measuring circuit 171. The time interval measuringcircuit 171 measures the fluctuation (jitter) of the reproductivesignal, and sends the measured result to the system controller 150. Thesystem controller 150 changes the recording power levels according tothe procedure described above with reference to FIGS. 3 and 4A-4C on thebasis of the measured result of the reproductive signal level in theamplifier 152 and the measured result of the jitter in the time intervalmeasuring circuit 171. Then, the system controller 150 sends thesuitable recording pattern to the signal processing circuit 154 again toform a recording mark string in the recording medium 100 using the newrecording power levels. In this manner, when the measurement of thereproductive signal level and reproductive jitter and the updating ofthe recording power level on the basis of the measured results thereofare repeated by the necessary number of times, the optimum recordingpower level for writing information in the given recording medium 100can be determined as occasion demands.

Further, the system controller 150 sends the suitable recording patternto the signal processing circuit 154 to form a recording mark string onthe recording medium 100. Then, the recording mark string is reproduced.The reproductive signal is two-valued by the slicer 170 and then sent tothe time interval measuring circuit 171. The time interval measuringcircuit 171 measures-the fluctuation (jitter) of the reproductive signaland sends the measured result to the system controller 150. When theobtained jitter is insufficient, the system controller 150 changes thevalues of the front and rear edge timing correction look-up tablesaccording to the procedure described above with reference to FIGS. 1, 3and 4A-4C. Then, the system controller 150 sends the suitable recordingpattern to the signal processing circuit 154 again to form a recordingmark string in the recording medium 100 using the new front and rearedge timing. In this manner, the measurement of the reproductive jitterand signal edge shifting and the updating of the correction values ofthe front and rear edge timing correction look-up tables on the basis ofthe results of the above measurement are repeated, so that the optimumlook-up tables for writing information in the given recording medium 100can be determined as occasion demands.

As described above, according to the present invention, the recordingpower levels and the recording correction look-up tables both of whichare always accurate can be obtained by the simple procedure even in thecase where the recording characteristic of the information recordingapparatus varies due to the change with the passage of time, the changeof temperature and so forth. Accordingly, there is a technical effectthat information can be always recorded stably.

(Third Embodiment)

An information recording method according to a third embodiment of thepresent invention will be described below. A mark string to be recordedin the recording medium will be described first with reference to FIGS.5A and 5B.

FIG. 5A shows a second state (hereinafter referred to as “mark”) and afirst state (hereinafter referred to as “space”) of the recording mediumboth of which are recorded on the recording medium. Let T be the periodof a clock signal (recording timing generating clock signal) whichoperates with a reference frequency when marks and spaces are recorded.Let v be the velocity of the energy beam relative to the recordingmedium. A small recording pattern “A” (first small recording pattern) iscomposed of a mark (first mark) with length avT, a space (first space)with length ivT following the first mark, a mark (second mark) withlength mvT following the first space, a space (second space) with lengthjvT following the second mark, and a mark (third mark) with length bvTfollowing the second space. A small recording pattern “B” (second smallrecording pattern) is composed of a space with length C₁vT, a mark withlength C₂vT following the space, a space with length C₃vT following themark, a mark with length C₄vT following the space, and a space withlength C₅vT following the mark. That is, the small recording pattern Bstarts from the first state (space) and ends with the first state(space) so that the first state (space) and the second state (mark)appear alternately by the finite number of times. The small recordingpattern A and the small recording pattern B following the smallrecording pattern A form a basic recording pattern. Here, a, i, m, j, band C₁ to C₅, which are parameters expressing the lengths of marks andspaces, are all natural numbers (positive integers).

A value obtained when a sum value obtained by the arithmetical additionof all space length parameters contained in the basic recording patternis subtracted from a sum value obtained by the arithmetical addition ofall mark length parameters contained in the basic recording pattern iscalled “Digital Sum Value (DSV)”. When the lengths of marks and spacesare adjusted so that the DSV of the basic recording pattern becomeszero, the dignity of the reproductive signal of the mark string isimproved.

A recording pattern is in a state in which the basic recording patternappears repeatedly. An example of the recording pattern will bedescribed below with reference to FIG. 5B. A recording pattern A1 (firstrecording pattern) is composed of a plurality of basic recordingpatterns. In the recording pattern A1, the various values of parameter jare prepared for the respective basic recording patterns (FIG. 5B showsthe case where j changes from j_(l) to j_(h)). The value of parameter jmay be changed at random in a range of from a lower limit to an upperlimit. A recording pattern B1 (second recording pattern) is alsocomposed of a plurality of basic recording patterns. In the recordingpattern B1, the various values of parameter i are prepared for therespective basic recording patterns (FIG. 5B shows the case where ichanges from i_(l) to i_(k)). The value of parameter i may be changed atrandom in a range of from a lower limit to an upper limit.

Reproductive signals obtained when the recording patterns A1 and B1recorded as shown in FIGS. 5A and 5B are reproduced, and processingmethods therefor will be described below with reference to FIGS. 6A and6B. Incidentally, for convenience' sake of description, the movementdirection of the energy beam relative to the recording medium is assumedto be from the left to the right in FIGS. 6A and 6B. Further, in eachmark, the mark border in a direction reverse to the movement directionof the energy beam is referred to as “front edge”, and the mark borderin the movement direction of the energy beam is referred to as “rearedge”.

FIG. 6A shows a part of the recording pattern A1 depicted in FIG. 5B anda reproductive signal corresponding to the recording pattern A1. Theposition where the reproductive signal crosses the slice level downwardshows the front edge in the reproductive signal. The time interval fromthe front edge of the avT-long mark (first mark) to the front edge ofthe mvT-long mark (second mark) is measured from the reproductive signalby a time interval measurer. A result obtained by the measurement is setas measured time T₁. The fact that the measured time T₁ does notcoincide with the time interval (a+i)T indicates the fact that the frontedge of the mvT-long mark (second mark) is not located in an appropriateposition. In this-manner, the position of the front edge of the mvT-longmark (second mark) can be measured from the reproductive signal.

It is now important that the length of the jvT-long space (second space)following the mvT-long mark (second mark) changes variously. There is afear that the irradiation with the energy beam for recording thebvT-long mark (third mark) may cause the fluctuation of the front edgeposition of the mvT-long mark (second mark). Further, the quantity ofthe fluctuation is also a function of the length of the jvT-long space(second space). Therefore, the length of the jvT-long space (secondspace) is changed variously so that an averaged quantity of thefluctuation is obtained. Accordingly, the measurement of the averagedfront edge position brings a technical effect that the mark edgeposition can be measured reliably even in the case where the front edgeposition of the mvT-long mark (second mark) is made to fluctuate by thebvT-long mark (third mark).

FIG. 6B shows a part of the recording pattern B1 depicted in FIG. 5B anda reproductive signal corresponding to the recording pattern B1. Thetime interval from the rear edge of the mvT-long mark (second mark) tothe rear edge of the bvT-long mark (third mark) is measured from thereproductive signal by the time interval measurer. A result obtained bythe measurement is set as measured time T₂. The fact that the measuredtime T₂ does not coincide with the time interval (j+b)T indicates thefact that the rear edge of the mvT-long mark (second mark) is notlocated in an appropriate position. In this manner, the position of therear edge of the mvT-long mark (second mark) can be measured from thereproductive signal.

It is now important that the length of the ivT-long space (first space)preceding the mvT-long mark (second mark) changes variously. There is afear that the irradiation with the energy beam for recording theavT-long mark (first mark) may cause the fluctuation of the rear edgeposition of the mvT-long mark (second mark). Further, the quantity ofthe fluctuation is also a function of the length of the ivT-long space(first space). Therefore, the length of the ivT-long space (first space)is changed variously so that an averaged quantity of the fluctuation isobtained. Accordingly, the measurement of the averaged rear edgeposition brings a technical effect-that the mark edge position can bemeasured reliably even in the case where the rear edge position of themvT-long mark (second mark) is made to fluctuate by the avT-long mark(first mark).

A method of accurately controlling the front and rear edges of any markwill be described below with reference to FIG. 1 in connection with aspecific example of irradiation with the energy beam for forming marksand spaces.

When T_(SFP) and T_(ELP) are changed in accordance with the combinationof the front and rear edges of the NRZI signal as described above in theinformation recording method according to the first embodiment of thepresent invention, the mark edge position can be always controlledaccurately. However, grasping the present mark edge position accuratelyis inevitable for shifting the mark edge position to a predeterminedplace. Therefore, the recording pattern shown in FIGS. 5A and 5B is usedso that the edge position is measured accurately by the edge positionmeasuring method shown in FIGS. 6A and 6B. When the look-up tables forT_(SFP) and T_(ELP) are generated or corrected on the basis of theresult of the edge position measurement, there is a technical effectthat the recording can be performed reliably so that all edge positionsare set in predetermined positions.

More specifically, when the value of one element in the front edgelook-up table (for example, the value of an element in the look-up tablein the case where the length of a mark (second mark) is MvT (in which Mis a natural number) and the length of'a space (first space) precedingthe mark is IvT (in which “I” is a natural number)) is to be examined,the recording pattern A1 shown in FIG. 5B is formed using the basicrecording patterns in which the values of parameters i and m for thesmall recording pattern A shown in FIG. 5A are made equal to “I” and M,respectively. The recording pattern A1 is recorded in the recordingmedium. Then, the time interval (measured time T₁) of the reproductivesignal from the front edge of the avT-long mark (first mark) to thefront edge of the MvT-long mark (second mark) is measured by the methodshown in FIG. 6A. When the measured time T₁ is longer than the timeinterval (a+I)T, the numerical value of the element in the look-up tableis reduced because the front edge of the MvT-long mark (second mark) isposterior to the predetermined position. That is, the value of T_(SFP)shown in FIG. 1 is adjusted to be reduced so that the first pulse startsin earlier timing. When the measured time T₁ is contrariwise shorterthan the time interval (a+I)T, the numerical value of the element in thelook-up table is increased because the front edge of the MvT-long mark(second mark) is prior to the predetermined position. That is, the valueof T_(SFP) shown in FIG. 1 is adjusted to be increased so that the firstpulse starts in later timing. By the aforementioned adjustment, thefront edge position of the mark (second mark) can be brought to thepredetermined position. When the aforementioned adjustment is applied toall elements in the front edge look-up table while the values of M and“I” are changed, there is a technical effect that the front edges can bealways positioned in predetermined positions stably even in the casewhere any NRZI signal combination is given. As a result, the reliabilityof the information storage can be improved.

As another example, when the value of one element in the rear edgelook-up table (for example, the value of an element in the look-up tablein the case where the length of a mark (second mark) is MvT (in which Mis a natural number) and the length of a space (second space) followingthe mark is JvT (in which J is a natural number)) is to be examined, therecording pattern B1 shown in FIG. 5B is formed using the basicrecording patterns in which the values of parameter j and m for thesmall recording pattern A shown in FIG. 5A are made equal to J and M,respectively. The recording pattern B1 is recorded in the recordingmedium. Then, the time interval (measured time T₂) of the reproductivesignal from the rear edge of the MvT-long mark (second mark) to the rearedge of the bvT-long mark (third mark) is measured by the method shownin FIG. 6B. When the measured time T₂ is longer than the time interval(b+J)T, the numerical value of the element in the look-up table isincreased because the rear edge of the MvT-long mark (second mark) isprior to the predetermined position. That is, the value of T_(ELP) shownin FIG. 1 is adjusted to be increased so that the last pulse ends inlater timing. When the measured time T₂ is contrariwise shorter than thetime interval (b+J)T, the numerical value of the element in the look-uptable is reduced because the rear edge of the MvT-long mark (secondmark) is posterior to the predetermined position. That is, the value ofT_(ELP) shown in FIG. 1 is adjusted to be reduced so that the last pulseends in earlier timing. By the aforementioned adjustment, the rear edgeposition of the mark (second mark) can be brought to the predeterminedposition. When the aforementioned adjustment is applied to all elementsin the rear edge look-up table while the values of M and J are changed,there is a technical effect that the rear edges can be always positionedin the predetermined positions stably even in the case where any NRZIsignal combination is given. As a result, the reliability of theinformation storage can be improved.

An information recording apparatus according to the third embodiment ofthe present invention will be described below. The configuration of theinformation recording apparatus according to this embodiment is the sameas that of the information recording apparatus according to the firstembodiment of the present invention shown in FIG. 2. Accordingly, theoperation of the information recording apparatus according to thisembodiment will be described below with reference to FIG. 2.

When the necessity of writing information occurs or before theinformation writing occurs, the look-up tables for controlling the frontand rear edges in the information writing mode may be optimized orupdated. In this case, the system controller 150 sends the recordingpattern A1 or B1 shown in FIG. 5B to the signal processing circuit 154to form the recording mark string shown in FIGS. 5A and 5B in therecording medium 100. Then, the recording mark string is reproduced. Thereproductive signal is two-valued by the slicer 170 and then sent to thetime interval measuring circuit 171. The time interval measuring circuit171 measures the time interval (measured time T₁) and the time interval(measured time T₂) shown in FIGS. 6A and 6B and sends the measurementresults to the system controller 150. The system controller 150 updatesthe look-up tables in accordance with the aforementioned procedure onthe basis of the measured time T₁ and the measured time T₂ received.Then, the system controller 150 sends the recording pattern A1 or B1 tothe signal processing circuit 154 again to form a recording mark stringin the recording medium 100 using the updated look-up tables.

In this manner, when the measurement of the measured time T₁ and themeasured time T₂ and the updating of the look-up tables on the basis ofthe measured results thereof are repeated by the necessary number oftimes, the optimum look-up tables for writing information in the givenrecording medium 100 can be generated as occasion demands. Accordingly,there is a technical effect that information can be always written onthe recording medium 100 stably and reliably.

Incidentally, a circuit having a time interval analyzer function may beconsidered as an example of the time interval measuring circuit 171. Asanother example, a first counter for counting the number of times whenthe distance between adjacent front edges is in a range of from(a+i−0.5)T to (a+i)T and a second counter for counting the number oftimes when the distance between adjacent front edges is in a range offrom (a+i)T to (a+i+0.5)T may be provided for the measurement of themeasured time T₁ shown in FIG. 6A. While the distance between the frontedges of marks is always monitored, a judgment may be made from thedifference between the frequency of the first counter and the frequencyof the second counter as to whether the measured time T₁ is longer thanthe predetermined time (a+i)T or not. That is, when the frequency of thefirst counter is higher than the frequency of the second counter, thejudgment may be made that the measured time T₁ is shorter than thepredetermined time (a+i)T. When the frequency of the first counter iscontrariwise lower than the frequency of the second counter, thejudgment may be made that the measured time T₁ is longer than thepredetermined time (a+i)T. Further, a third counter for counting thenumber of times by which the distance between adjacent rear edges is ina range of from (b+j−0.5)T to (b+j)T and a fourth counter for countingthe number of times by which the distance between adjacent rear edges isin a range of from (b+j)T to (b+j+0.5)T may be provided for themeasurement of the measured time T₂ shown in FIG. 6B. While the distancebetween the rear edges of marks is always monitored, a judgment may bemade from the difference between the frequency of the third counter andthe frequency of the fourth counter as to whether the measured time T₂is longer than the predetermined time (b+j)T or not. That is, when thefrequency of the third counter is higher than the frequency of thefourth counter, the judgment may be made that the measured time T₂ isshorter than the predetermined time (b+j)T. When the frequency of thethird counter is contrariwise lower than the frequency of the fourthcounter, the judgment may be made that the measured time T₂ is longerthan the predetermined time (b+j)T. The configuration of the timemeasurement based on the comparison between the frequencies of thecounters can be more simplified than the configuration of the timeinterval analyzer. Consequently, there is a technical effect that thereliability is high because the configuration is simple.

Specific examples of the recording mark string will be described belowwhile the DVD-RAM is taken as an example. In the recording mark string,it is preferable that the DSV is zero. It is also preferable that anyunnecessary mark edge interval is not mixed in the mark edge interval tobe measured. Recording mark strings shown in FIGS. 7A and 7B areconsidered as specific examples of the recording mark string. In the twospecific examples of the basic recording pattern shown in FIGS. 7A and7B, it is assumed that each of parameters i, m and j is an integer in arange of from 3 to 6, inclusively. When the recording pattern A1 or B1shown in FIG. 5B is formed using the aforementioned basic recordingpattern, the DSV becomes zero and any unnecessary mark edge interval isprevented from overlapping the mark edge interval to be measured.Accordingly, there is a technical effect that the mark edge positionscan be measured accurately.

The case where the recording patterns A1 and B1 shown in FIG. 5B aremixed will be described below while the DVD-RAM is taken as an example.It is prerequisite in this case that a recording pattern using the basicrecording pattern shown in FIG. 7A or a recording pattern using thebasic recording pattern shown in FIG. 7B is used. That is, in the basicrecording pattern shown in FIG. 7B, parameters i and j are changedvariously while parameter m is fixed so that a plurality of basicrecording patterns are formed. The basic recording patterns areconnected to one another to thereby form a recording pattern C.Incidentally, it is now assumed that the basic recording patterns in therecording pattern C contain all combinations of parameters i and j inthe condition that each of the parameters i and j is in a range of from3 to 6, inclusively.

FIG. 8 shows a specific example of the recording mark string formed inthe aforementioned manner. This specific example is provided in the caseof m=6.The numeral written in a quadrilateral frame indicates aparameter of the length of the mark. The actual length of the mark isobtained when the numeral written in the quadrilateral frame ismultiplied by vT. Further, the numeral written outside the quadrilateralframe indicates a parameter of the length of the space. The actuallength of the space is obtained when the numeral written outside thequadrilateral frame is multiplied by vT. As the mark-space string islong, it is expressed so as to be folded. The mark-space string is shownso that the mark-space string starts from a mark in the left uppercorner of FIG. 8 and that marks and spaces are arranged alternately inthe rightward direction in FIG. 8. A space at the right end of a line inFIG. 8 is followed by a mark at the left end of the next line. A spaceat the right end of the last line in FIG. 8 is the last in the recordingpattern C. This recording pattern is recorded repeatedly by thenecessary number of times. The recording pattern is reproduced.

The front edge interval is measured. The edge position to make the frontedge interval near 13T is the front edge position of a 6T-long mark inthe case where the length of a space preceding the mark is 3T. Further,the edge position to make the front edge interval near 14T is the frontedge position of a 6T-long mark in the case where the length of a spacepreceding the mark is 4T. Further, the edge position to make the frontedge interval near 15T is the front edge position of a 6T-long mark inthe case where the length of a space preceding the mark is 5T. Further,the edge position to make the front edge interval near 16T is the frontedge position of a 6T-long mark in the case where the length of a spacepreceding the mark is 6T.

The rear edge interval is also measured. The edge position to make therear edge interval near 13T is the rear edge position of a 6T-long markin the case where the length of a space following the mark is 3T.Further, the edge position to make the rear edge interval near 14T isthe rear edge position of a 6T-long mark in the case where the length ofa space following the mark is 4T. Further, the edge position to make therear edge interval near 15T is the rear edge position of a 6T-long markin the case where the length of a space following the mark is 5T.Further, the edge position to make the rear edge interval near 16T isthe rear edge position of a 6T-long mark in the case where the length ofa space following the mark is 6T.

When such a mark-space string as shown in FIGS. 7A and 7B is used asdescribed above, the front and rear edges of the mark can be measuredsimultaneously on the basis of the repetition of the same recordingpattern C. Further, the DSV is zero, so that the edge positionscorresponding to the various combinations of the preceding and followingspaces with respect to the given mark length can be measured all atonce. Accordingly, there is a technical effect that the edge positionscan be measured easily and accurately.

FIG. 9 shows a recording mark string in the case of m=5.The way ofarranging the marks and the spaces is the same as in FIG. 8. Thisrecording pattern is recorded repeatedly by the necessary number oftimes and then reproduced.

The front edge interval is measured. The edge position to make the frontedge interval near 13T is the front edge position of a 5T-long mark inthe case where the length of a space preceding the mark is 3T. Further,the edge position to make the front edge interval near 14T is the frontedge position of a 5T-long mark in the case where the length of a spacepreceding the mark is 4T. Further, the edge position to make the frontedge interval near 15T is the front edge position of a 5T-long mark inthe case where the length of a space preceding the mark is 5T. Further,the edge position to make the front edge interval near 16T is the frontedge position of a 5T-long mark in the case where the length of a spacepreceding the mark is 6T.

The rear edge interval is also measured. The edge position to make therear edge interval near 13T is the rear edge position of a 5T-long markin the case where the length of a space following the mark is 3T.Further, the edge position to make the rear edge interval near 14T isthe rear edge position of a 5T-long mark in the case where the length ofa space following the mark is 4T. Further, the edge position to make therear edge interval near 15T is the rear edge position of a 5T-long markin the case where the length of a space following the mark is 5T.Further, the edge position to make the rear edge interval near 16T isthe rear edge position of a 5T-long mark in the case where the length ofa space following the mark is 6T.

FIG. 10 shows a recording mark string in the case of m=4.The way ofarranging the marks and the spaces is the same as in FIG. 8. Thisrecording pattern is recorded repeatedly by the necessary number oftimes and then reproduced.

The front edge interval is measured. The edge position to make the frontedge interval near 13T is the front edge position of a 4T-long mark inthe case where the length of a space preceding the mark is 3T. Further,the edge position to make the front edge interval near 14T is the frontedge position of a 4T-long mark in the case where the length of a spacepreceding the mark is 4T. Further, the edge position to make the frontedge interval near 15T is the front edge position of a 4T-long mark inthe case where the length of a space preceding the mark is 5T. Further,the edge position to make the front edge interval near 16T is the frontedge position of a 4T-long mark in the case where the length of a spacepreceding the mark is 6T.

The rear edge interval is also measured. The edge position to make therear edge interval near 13T is the rear edge position of a 4T-long markin the case where the length of a space following the mark is 3T.Further, the edge position to make the rear edge interval near 14T isthe rear edge position of a 4T-long mark in the case where the length ofa space following the mark is 4T. Further, the edge position to make therear edge interval near 15T is the rear edge position of a 4T-long markin the case where the length of a space following the mark is 5T.Further, the edge position to make the rear edge interval near 16T isthe rear edge position of a 4T-long mark in the case where the length ofa space following the mark is 6T.

FIG. 11 shows a recording mark string in the case of m=3.The way ofarranging the marks and the spaces is the same as in FIG. 8. Thisrecording pattern is recorded repeatedly by the necessary number oftimes and then reproduced.

The front edge interval is measured. The edge position to make the frontedge interval near 13T is the front edge position of a 3T-long mark inthe case where the length of a space preceding the mark is 3T. Further,the edge position to make the front edge interval near 14T is the frontedge position of a 3T-long mark in the case where the length of a spacepreceding the mark is 4T. Further, the edge position to make the frontedge interval near 15T is the front edge position of a 3T-long mark inthe case where the length of a space preceding the mark is 5T. Further,the edge position to make the front edge interval near 16T is the frontedge position of a 3T-long mark in the case where the length of a spacepreceding the mark is 6T.

The rear edge interval is also measured. The edge position to make therear edge interval near 13T is the rear edge position of a 3T-long markin the case where the length of a space following the mark is 3T.Further, the edge position to make the rear edge interval near 14T isthe rear edge position of a 3T-long mark in the case where the length ofa space following the mark is 4T. Further, the edge position to make therear edge interval near 15T is the rear edge position of a 3T-long markin the case where the length of a space following the mark is 5T.Further, the edge position to make the rear edge interval near 16T isthe rear edge position of a 3T-long mark in the case where the length ofa space following the mark is 6T.

In the recording pattern described above with reference to FIGS. 8-11,the edge interval having the same length may be always measuredirrespective of the value of m as follows. The edge interval of 13T isalways measured when the length of the preceding/following space is 3T.The edge interval of 14T is always measured when the length of thepreceding/following space is 4T. The edge interval of 15T is alwaysmeasured when the length of the preceding/following space is 5T. Theedge interval of 16T is always measured when the length of thepreceding/following space is 6T. That is, only the measurement of thesame edge interval which does not change irrespective of m issufficient. Accordingly, there is a technical effect that themeasurement is simplified and the edge positions can be detected easilyand accurately.

A processing method for evaluating the edge positions by a simplecircuit system on the basis of the recording pattern shown in FIGS. 8-11will be described below. The following five kinds of counters are usedfor monitoring the distance between adjacent front edges. That is, thereare used a first counter for counting the number of times by which thedistance between the front edges is in a range of from a length of 11.5Tto a length of 12.5T, a second counter for counting the number of timeswhen the distance between the front edges is in a time range of from alength of 12.5T to a length of 13.5T, a third counter for counting thenumber of times when the distance between the front edges is in a timerange of from a length of 13.5T to a length of 14.5T, a fourth counterfor counting the number of times when the distance between the frontedges is in a time range of from a length of 14.5T to a length of 15.5Tand a fifth counter for counting the number of times when the distancebetween the front edges is in a time range of from a length of 15.5T toa length of 16.5T. The front edge position in the case where the lengthof the preceding space is 3T is estimated on the basis of the differencebetween the value of the first counter and the value of the secondcounter. The front edge position in the case where the length of thepreceding space is 4T is estimated on the basis of the differencebetween the value of the second counter and the value of the thirdcounter. The front edge position in the case where the length of thepreceding space is 5T is estimated on the basis of the differencebetween the value of the third counter and the value of the fourthcounter. The front edge position in the case where the length of thepreceding space is 6T is estimated on the basis of the differencebetween the value of the fourth counter and the value of the fifthcounter.

Then, the distance between adjacent rear edges is monitored so that theedge intervals are measured by use of the aforementioned first, second,third, fourth and fifth counters. The rear edge position in the casewhere the length of the following space is 3T is estimated on the basisof the difference between the value of the first counter and the valueof the second counter. The rear edge position in the case where thelength of the following space is 4T is estimated on the basis of thedifference between the value of the second counter and the value of thethird counter. The rear edge position in the case where the length ofthe following space is 5T is estimated on the basis of the differencebetween the value of the third counter and the value of the fourthcounter. The rear edge position in the case where the length of thefollowing space is 6T is estimated on the basis of the differencebetween the value of the fourth counter and the value of the fifthcounter.

The use of the aforementioned configuration brings a technical effectthat the look-up tables for controlling the mark edge positions can bedetermined accurately in accordance with all combinations of the frontand rear edges of the NRZI signal when the five kinds of simple countersare prepared.

Although the basic recording pattern shown in FIG. 7B is used in thedescription with reference to FIGS. 8-11, the same effect as describedabove can be obtained also in the case where the basic recording patternshown in FIG. 7A is used for forming a recording mark string in the samemanner as described in FIGS. 8-11. In this case, there is a technicaleffect that the total number of the marks and spaces is reduced, so thatthe recording pattern is generated easily.

As described above, according to the present invention, the recordingmark edges can be always positioned in the predetermined positionsstably even in the case where the high-density recording is performed sothat the shortest recording mark length is not larger than the radius ofthe recording spot. Accordingly, there is a technical effect thatinformation can be always recorded on the recording medium stably andreliably.

1. An information recording apparatus comprising: an energy beamgenerator for generating an energy beam; a power adjusting mechanism forsetting a power level of said energy beam to a first power level stateand a second power level state which is higher than said first powerlevel state; and a circuit for generating a basic recording pattern torecord a recording medium; wherein when a period of a recording timinggenerating clock in a recording mode is T, and a relative velocity ofsaid energy beam and said recording medium is v, said circuit forms: asequence of said second power level state with a length avT so as torecord a first mark, said first power level state with a length ivT soas to record a first space following said first mark, said second powerlevel state with a length mvT so as to record a second mark followingsaid first space, said first power level state with a length jvT so asto record a second space following said second mark, and said secondpower level state with a length bvT so as to record a third markfollowing said second space as a first small recording pattern; forms asequence which starts with said first power level state and ends withsaid first power level state while said first and second power levelstates appear alternately a finite number of times, as a second smallrecording pattern; forms the second small recording pattern followingthe first small recording pattern as a basic recording pattern; forms arecording pattern in which the basic recording patterns are repeated;forms the recording pattern which comprises the basic recording patternsobtained by changing a parameter j variously while parameters a, i and mare fixed, as a first recording pattern, the parameters a, i, m and jbeing natural numbers; and forms the recording pattern which comprisesthe basic recording patterns obtained by changing the parameter ivariously while parameters b and said parameters j and m are fixed, as asecond recording pattern, the parameter b being a natural number.